Ethenolysis is a specific cross metathesis reaction between an internal olefin and ethylene to produce terminal olefins. Scheme 1 demonstrates the ethenolysis reaction:
Examples of ethenolysis include the conversion of a mixture of ethylene and 2-butene into propene (as in the Phillips triolefin process and the Meta-4 process developed by the Institut Français du Pétrole), and the conversion of a mixture of ethylene and 2,4,4-trimethyl-2-pentene into neohexene. These processes typically use heterogeneous ill-defined olefin metathesis catalysts based on tungsten and rhenium oxides and which are not compatible with air, water, oxygenates, and many functional groups. The ethenolysis reaction has also been implemented in the conversion of seed oil-derived substrates such as fatty acid methyl esters (FAME) into terminally unsaturated carboxylic acids (e.g., 9-decenoic acid) and terminal olefins (e.g., 1-decene). The ethenolysis of FAME was originally performed with a heterogeneous, ill-defined rhenium catalyst to give turnover numbers (TON) of about 100. The so-called “first generation” Grubbs catalysts such as Cl2(PCy3)2Ru═CH—CH═CPh2, Cl2(PCy3)2Ru═CHPh (“C823”), and complexes that contain bicyclic phosphines, as well as first generation Grubbs-Hoveyda catalyst (“C601”), have been used in the ethenolysis of vegetable oil-derived materials. The production of 1-octene from linoleic acid using an enzyme-mediated isomerization reaction, followed by a metathesis reaction using ethylene and various metathesis catalysts, has also been described. However, the conjugation present in these reactants necessitated a high catalyst loading and often resulted in a relatively low yield of terminal olefin products.
It is therefore desirable to provide a convenient and effective route for the production of terminal olefins. Compared with known metathesis methods, an ideal process would: substantially reduce the amount of catalyst that is needed for the cross-metathesis reaction; provide a high degree of selectivity for the preparation of terminal olefins from internal olefins; and allow the use of a mixture of internal olefins from a variety of sources. An ideal process would also not require isomerization of the olefinic substrate prior to the metathesis reaction, and an ideal process would allow for the preparation of terminal olefins directly from seed oils and from the component materials of seed oils, or from non-isomerized derivatives of seed oils.